Different types of acoustic devices have been used through the years. One type of device is a microphone. In a microelectromechanical system (MEMS) microphone, a MEMS die includes a diaphragm and a back plate. The MEMS die is supported by a base and enclosed by a housing (e.g., a cup or cover with walls). A port may extend through the base (for a bottom port device) or through the top of the housing (for a top port device) or through the side of the housing (for a side port device). In any case, sound energy traverses through the port, deforms the diaphragm and creates a changing electrical capacitance between the diaphragm and the back-plate, which creates an electrical signal. Microphones are deployed in various types of devices such as personal computers, cellular phones and tablets.
One type of a MEMS microphone utilizes a free plate diaphragm. The biased free plate diaphragm typically sits on support posts located along the periphery of the diaphragm. The support posts restrain the movement of the diaphragm. Free plate diaphragms tend to have a high mechanical compliance. Consequently, designs that utilize free plate diaphragms may suffer from high total harmonic distortion (THD) levels, particularly when operating at high sound pressure levels (SPLs).
All of these problems have resulted in some user dissatisfaction with previous approaches.
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